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M. Dunbar



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    MA13 - Modern Technologies and Biological Factors in Radiotherapy (ID 395)

    • Event: WCLC 2016
    • Type: Mini Oral Session
    • Track: Radiotherapy
    • Presentations: 1
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      MA13.01 - Markerless Tumour Tracking during Lung Radiotherapy Using Intrafraction X-Ray Imaging (ID 5533)

      16:00 - 16:06  |  Author(s): M. Dunbar

      • Abstract
      • Presentation
      • Slides

      Background:
      Lung tumours often exhibit large and unpredictable motion that can severely compromise radiotherapy outcomes. Markerless tumour tracking can enable wide access to motion-adaptive radiotherapy, negating the risks and costs associated with implanting markers. The main barrier to markerless tumour tracking is the inferior tumor visibility on x-ray images due to overlapping anatomic structures. The aim of this study is to develop a markerless tumor tracking method for lung radiotherapy using intrafraction x-ray imaging.

      Methods:
      The markerless tumour tracking method (Figure1a) consists of four steps: (1) Building a tumour and anatomic model from the cone-beam CT (CBCT) acquired prior to treatment, (2) Using the anatomic model to remove the contribution of anatomic structures on intrafraction x-ray images, (3) Locating the tumour on the intrafraction 2D x-ray image via template matching using the tumour model, (4) Determining the tumour 3D position by a Kalman filter. The proposed method was retrospectively validated on (i) 11 CBCT scans from four patients with central tumours, and (ii) a kV fluoroscopic scan during a stereotactic ablative radiotherapy (SABR) treatment from the Light SABR trial (NCT02514512). Tracking errors were estimated using the motions of markers or beacons implanted near the tumours. Figure 1



      Results:
      Markerless tumour tracking successfully tracked tumours in all cases at every imaging angle. The mean 3D tracking error ranged from 1.8-4.1mm for the 11 CBCT scans, and was 3.0mm for the SABR case. Compared with the current standard of care, i.e. a single estimation of tumour position prior to treatment from the pre-treatment CBCT, markerless tumour tracking reduced tumour localization error by 0.9-7.9mm. Tracking errors in the left-right, superior-inferior, and anterior-posterior directions are shown in Figure1b.

      Conclusion:
      A markerless tumour tracking method was developed and shown to improve tumour localization accuracy in 12 lung cancer cases. This method can potentially enable wide access to motion-adaptive radiotherapy.

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